In nature, plants often grow in two external adverse conditions including biological and abiotic stress, the former one contains the invasion of fungi, bacteria, viruses and other microorganisms or insects, while the latter contains cold damage, salt damage, light damage and other non-biology stress. The special external structures of plants, such as cuticular layer, cork layer, or wax membrane, provide plants an early barrier of physical defense and protect fragile tissue from external environment. Plants can detect the existence of pathogens directly through cell membrane receptors such as receptor-like kinase and histidine kinase, or detect indirectly through some inducers such as oligosaccharide, lipid polysaccharides, glycopeptides and peptides from plants or pathogens, to trigger a cascade of defense mechanisms, including the generation of defense messages, the accumulation of antibiotics or disease-related proteins. At present, these defences deem to have the following physiological functions: 1. repairing the damaged plant tissues, 2. involving in message regulation of defense mechanism, 3. producing substances which can inhibit pathogens, insects, or other potential harmful substance to the plant growth, 4. regulating plant metabolism. Kwon S J et al. also published that GDLS lipase-like 1 regulates systemic resistance which is dependent on ethylene signaling.
With the understanding of the plant pathogens and molecular level of defense mechanism, human can apply the molecular genetics as a tool to breeding in order to achieve effective control of plant pest. The farmers in the United Kingdom use weak tobacco mosaic virus for greenhouse tomato to prevent damage caused by virus for a long time. Brazilian farmers use citrus tristeza virus which do not produce symptoms to protect citrus plants and New Zealand farmers use apple mosaic virus to do similar prevention work to avoid substantial losses caused by virus infection. In the end of the twentieth century, researchers have found that plants which express special virus protein can prevent disease. However, the method cannot defense exclusively and may probably generate new virus. Following researchers try to find the pathogen defense mechanism in plants and improve the strength of reaction to create plants resistant to pests. TW 149283 claims the use of sweet potato sporamic gene inserted in to a vector and transform into Agrobateria, then use Agrobacteria as a medium to infect plants to enhance the ability of insect-resistance. Sarowar S. et al. published in 2008 pointed out that overexpression of lipid transfer protein (LTP) can elevate plants resistance to pathogens, and the function of LTP is long-distance systemic signaling in plants (Sarowar S. et al., Plant Cell Rep. 28 (2009) pp. 419-427).
Bupleurum kaoi Liu, Chao et Chuang is a species endemic to Taiwan that has 12 pairs of chromosomes and a genome size of about 7.3×108 bp per copy. Bupleurum roots have been reported to possess anti-inflammatory activity (Navarro P. et al., Life Sci. 68 (2001) 1199-1206) and antihepatotoxic effects. Extracting pharmacological agents from roots of intact plants or from tissue-cultured roots is of interest.
Ethylene-responsive element binding factors (ERFs) are a member of downstream ethylene signaling pathway, which can enhance plant resistance against pathogen.